KEF LS50 thoughts

[PENG]

I've not followed the more technical discussion here closely (time, you know) but I just want to mention that the UK speaker industry has a long history of allowing, you might even say using, cabinet resonances to voice a loudspeaker. This is in contrast to the North American practice of hunting down and (ideally) eliminating all enclosure contributions (the Japanese are sometimes even more fastidious in that regard, if their better speaker products {as in 'intended for serious HiFi Audio buyers'} are considered).

I highly recommend you read the 23 page white paper that among other things, also describes the effort they put in dealing with cabinet related resonance. Judging from the highly technical contents, I believe the paper was written by real engineers, or at least they were involved heavily. Again, FEA/BEA are very effective computerized tools for structural analysis that I am sure are used every second in the real world in all sorts of applications. I am happy to know KEF actually use it to help in the design of the LS50 and their reference series speakers.

 

[Johnny2Bad]

I highly recommend you read the 23 page white paper that among other things, also describes the effort they put in dealing with cabinet related resonance. Judging from the highly technical contents, I believe the paper was written by real engineers, or at least they were involved heavily. Again, FEA/BEA are very effective computerized tools for structural analysis that I am sure are used every second in the real world in all sorts of applications. I am happy to know KEF actually use it to help in the design of the LS50 and their reference series speakers.

I am quite busy at the moment, but I will try to find some time later in the week. KEF in many ways is not your typical "British" speaker company, so it might be an interesting read in that respect.

 

[KEW]

So I went back and set up my system with my Ascend RAAL towers yesterday and BAMMM!! What a sound. It's been a while since I had them hooked up and was like wow.. Maybe I don't need anything else. Now to make them perfect, just make them bigger with 8 in woofers so I don't need to use my sub.

What's that? You say you are gonna order a pair of Philharmonic BMR's?

(Yeah, it is only a 7" woofer, but a capable one; -2dB at 32Hz; vs. 41Hz at -3dB for the Sierra! Based on Ascends claims for the Sierra FR in-room, the BMR should hit the low 20's in-room!)

 

[Dennis Murphy]

What's that? You say you are gonna order a pair of Philharmonic BMR's?

(Yeah, it is only a 7" woofer, but a capable one; -2dB at 32Hz; vs. 41Hz at -3dB for the Sierra! Based on Ascends claims for the Sierra FR in-room, the BMR should hit the low 20's in-room!)

I wish. The .75 cu ft version I'm currently selling doesn't have any useful response below about 32 Hz. I need to clarify that on my website. I would say the -3 dB point is more like 34-35 Hz, and, as with any ported system, will drop like a stone below that point. The only speaker I make that can make it into the low 20's in-room is the Philharmonic 3.

 

[Beave]

Dr. Toole himself has stated that the NRC measurements for the LS50 show a resonance.

I'd be a fool to argue with him.

So let me do just that!

Chart B, the off-axis frequency response plots, seem to show an off-axis resonant peak centered at 2kHz.

But if you disregard that little drop in the 3-4kHz range of those curves, that peak would no longer look so much like a resonant peak and instead would look a lot like a directivity mismatch between the woofer and tweeter (something that shows up in lots of speakers measured at the NRC).

Other than that little dip around 3-4kHz, which might be a diffraction effect, the output is well-controlled and smoothly dropping from 2kHz to 20kHz. And 2kHz is very near the crossover frequency.

Any chance that's all that's going on here - and that it just looks like something it isn't?

 

[TheWarrior]

Any chance that's all that's going on here - and that it just looks like something it isn't?

It's an anechoic measurement - not an ink blot!

 

[Steve81]

Chart B, the off-axis frequency response plots, seem to show an off-axis resonant peak centered at 2kHz.

But if you disregard that little drop in the 3-4kHz range of those curves, that peak would no longer look so much like a resonant peak and instead would look a lot like a directivity mismatch between the woofer and tweeter (something that shows up in lots of speakers measured at the NRC).

It's an anechoic measurement - not an ink blot!

I'm not sure its a problem with directivity or resonance based on the whole set of NRC measurements.

Consider a cleaner view of the on axis FR from the distortion graph:

It seems to me the tweeter is clearly tipping things up between 2kHz and 5kHz relative to the mid/woofer level. It also seems to me that off axis, those relative proportions are maintained pretty well.

Drop the tweeter level 4dB or so, and all you'd really see is that off axis dip around 4kHz, and the rise afterwards as a result of the tangerine phase plug.

 

[TheWarrior]

Drop the tweeter level 4dB or so, and all you'd really see is that off axis dip around 4kHz, and the rise afterwards as a result of the tangerine phase plug.

Correct, this is not an ink blot. If the only rebuttal's at this point are to say, "well if you ignore the measurement" then this thread is truly finished.

 

[Steve81]

Correct, this is not an ink blot. If the only rebuttal's at this point are to say, "well if you ignore the measurement" then this thread is truly finished.

Who said anything about ignoring measurements? I said if you take into account the actual on axis measurement, the off axis measurements make sense, without need to introduce other factors like resonances and directivity mismatches. The LS50 has its own particular voicing, that much is clear, and it probably won't appeal to everyone. If you want an "unvoiced" version, that's effectively where the R100 sits.

 

[TheWarrior]

Who said anything about ignoring measurements? I said if you take into account the actual on axis measurement, the off axis measurements make sense, without need to introduce other factors like resonances and directivity mismatches. The LS50 has its own particular voicing, that much is clear, and it probably won't appeal to everyone. If you want an "unvoiced" version, that's effectively where the R100 sits.

Beave said it directly, and I felt you alluded to it in the sentence I quoted.

We've already confirmed that we have incomplete data to really narrow down the cause. So floating ideas on what could be done differently with incomplete data is really beating this thread into a pulp.

BTW the 'tangerine phase plug' is the tweeter which, given the very respectable high frequency extension, does seem to minimize propagation loss in the upper octave with it's waveguide.

 

[ematthews]

I wish. The .75 cu ft version I'm currently selling doesn't have any useful response below about 32 Hz. I need to clarify that on my website. I would say the -3 dB point is more like 34-35 Hz, and, as with any ported system, will drop like a stone below that point. The only speaker I make that can make it into the low 20's in-room is the Philharmonic 3.

Well. Maybe those 3's are in my plan now..

 

[TheWarrior]

Well. Maybe those 3's are in my plan now..

They are a marvel!

 

[Steve81]

We've already confirmed that we have incomplete data to really narrow down the cause. So floating ideas on what could be done differently with incomplete data is really beating this thread into a pulp.

It's not a matter of what could be done differently. It is what was done differently with the very similar (in terms of basic hardware) R100, which was also measured by the NRC. Its on axis measurement is smoother around the XO point than the LS50s, and its off axis plot is correspondingly smoother as well.

 

[KEW]

No sir, I only said Floyd pointed me to the graphs, after I asked him what could be causing the issue I was hearing.

How would you describe the issue you were hearing?

I ask because it would not be my intuition to associate what I heard with a 2 kHz resonance (not that I am very experienced correlating perception to actual characteristics of a speaker) and it sounds like Floyd did make such a connection with your description vs measurements?

 

[Steve81]

How would you describe the issue you were hearing?

Hey Kurt,

Out of curiosity, did you try a "crossfire" setup with the LS50s? That was one of (KEF superfan) DS21's setup tips for them, so just wondering what if any effect that may have had for them.

 

[KEW]

Hey Kurt,

Out of curiosity, did you try a "crossfire" setup with the LS50s? That was one of (KEF superfan) DS21's setup tips for them, so just wondering what if any effect that may have had for them.

Sorry, I did not.

It may be a stretch to make any inferences from another speaker, but...
I do run the Klipsch RF-82 ii's using that type of "crossfire" setup.
IME, for that speaker in that configuration, it doesn't effect the sound within the confines of the LP so much, but it does make for improved consistency as I move around the room.

 

[TheWarrior]

It's not a matter of what could be done differently. It is what was done differently with the very similar (in terms of basic hardware) R100, which was also measured by the NRC. Its on axis measurement is smoother around the XO point than the LS50s, and its off axis plot is correspondingly smoother as well.

View attachment 23504
View attachment 23505

Smooth is usually described with a speaker's ability to maintain a +/-3dB variation across it's operating range. Neither of these speakers offer that, and the off axis of the R100 suggests there may be a resonance there as well, considering the blurring of the measurements 0-30deg around 1.5khz and 2.2 kHz - whatever that is, it is not smooth!

How would you describe the issue you were hearing?

I ask because it would not be my intuition to associate what I heard with a 2 kHz resonance (not that I am very experienced correlating perception to actual characteristics of a speaker) and it sounds like Floyd did make such a connection with your description vs measurements?

It was the absence of sounds from sung voices and some brass or percussive instruments did not sound accurate.

 

[Steve81]

Smooth is usually described with a speaker's ability to maintain a +/-3dB variation across it's operating range. Neither of these speakers offer that

Are you having fun putting words in my mouth? I said that compared to the LS50, the R100's on axis response was smoother around the XO point, and consequently, there is no large peak off axis in that range as seen with the LS50.

and the off axis of the R100 suggests there may be a resonance there as well, considering the blurring of the measurements 0-30deg around 1.5khz and 2.2 kHz - whatever that is, it is not smooth!

I don't know what you're looking at, but I see nothing on the R100's 0-30 degree charts suggesting a significant problem with resonance.

 

[ematthews]

They are a marvel!

The issue I have right now. I am going to sell off a lot of what I own except the Ascends and look for a tower to rule them all and be done. RBH Sound are also in the mix since I own the SX-6300R and my only complaint was a little muddy on the low end and thought they needed a little more detail in the upper range. Well the new ones have addressed both. Lot's of options out there and I am going to be patient.

 

[KEW]

The issue I have right now. I am going to sell off a lot of what I own except the Ascends and look for a tower to rule them all and be done. RBH Sound are also in the mix since I own the SX-6300R and my only complaint was a little muddy on the low end and thought they needed a little more detail in the upper range. Well the new ones have addressed both. Lot's of options out there and I am going to be patient.

Have you tried swapping rooms between the Sierra's and the RBH's?
It'd be interesting to see if that would address any of your complaints.